The piezoelectric motion actuator is a motion actuator that provides positioning control with a resolution of the nanometer level. The piezoelectric motion actuator may be used in all kinds of nano-level motion control, nanofabrication and nano-handling. Under the existing technologies, some piezoelectric motion actuator may provide positioning control at the sub-nanometer level.
There are typically three types of driving mode for linear motors using piezoelectric motion actuator. They are the inchworm, the inertial drive and the frictional drive. An inchworm consists of a pair of clampers, a stretcher and a shaft. The clampers are used to clamp the shaft and the stretcher generates a displacement motion to the shaft to drive the shaft. By running the inchworm with a succession of clamp-stretch-unclamp-unstretch cycles, an incremental linear movement with a step size of submicron or smaller may be generated.
In the inertial drive mode, there are two different operation principles. One is the “impact drive” which consists of a main body, an actuator, an inertial mass and a guiding surface. The main body is positioned on a guiding surface. The main body and the inertial mass are attached on two ends of the actuator, with the inertial mass not contacting the surface. The actuator makes a slow extension followed by a rapid contraction. The impulsive inertial force results in a step-like and backlash-free movement of the main body. The other driving principle is the “stick-slip-effect” drive, which consists of a main body, a base piece, shear motion piezoelectric elements in between and a mechanism that provides a preloading force for the above elements. The main body is first moved slowly in one direction relative to the base piece by deforming the piezoelectric elements (stick). Then the piezoelectric elements are undeformed suddenly and the main body remains almost unmoved (relative to the base piece) due to its large inertia being able to overcome the small frictional force (slip). In this manner, the main body makes a step-like linear motion relative to the base piece by repeatedly driving the piezoelectric elements with the same cycle. The theoretical resolution of the inertial drive is less than 1 nm, while its experimental resolution depends on the mass and the interface of the contacting surfaces. The mechanical structure of the inertial drive is simple, compact and easy to fabricate, while its major drawback is the small carry mass if the linear motion is in the vertical direction.
A friction drive drives a main body in a way different from that of the inertial drive. The piezoelectric elements deform sequentially and later undeformed simultaneously. When all the piezoelectric elements undeform, the friction force drives the main body to move a short distance. Pan et al. proposed a friction motion actuator having six piezoelectric elements which hold a triangular shaft in position. See S. H. Pan et al., “The refrigerator based very low temperature scanning tunneling microscope”, Review of Scientific Instruments, Vol. 70, pp 1459-1463, February 1999. To move one step, the six elements are deformed in sequence along the axial direction of the shaft and are undeformed simultaneously to drive the shaft. The step size of the friction drive is 200 nm at room temperature and is about 30 nm at temperature below 4K. The entire structure of the friction drive is rigid and stable. It can carry a load of several kilograms when the linear motion is along the vertical direction. Its walking speed, however, is slow and the structure is tedious to build.